Apparatus and method for grinding



Nov. 30, 1954 G. E. coMsTocK, 3RD, ET AL 7 APPARATUS AND METHOD FORGRINDING 5 Sheets-Sheet 1 Filed Dec. 29. 1952 IN V EN ITORS 5217255 .6.fiaMsmzKju 560F515 E/FUMFTUN JR.

N 1954 G. E. COMSTOCK, 3RD. ET AL 2,69

APPARATUS AND METHOD FOR GRINDING 5 Sheets-Sheet 2 Filed Dec. 29, 1952INVEN TORS GED/FEE E. CUMS mpKjr Nov. 30, 1954 e. E. COMSTOCK, 3RD, ETAL2, ,478

APPARATUS AND METHOD FOR GRINDING Filed Dec. 29, 1952 5 Sheets-Sheet 3Fig.6 H98 INVENTORS GEURGE EUM5T0cK3r GEURGE C/wMPTa/v JR.

ATTO/Z 1954 G. E. cOMsTocK, 3RD. ET AL 2,695,478

APPARATUS AND METHOD FOR GRINDING Filed Dec. 29, 1952 5 Sheets-Sheet 474 T INVENTORS GEUR'GE E. Emma/(3Y4 GEUR'EE CEUMPTUN JR.

HTTOEN Nov. 30, 1954 G. E. COMSVTOCK, 3RD, ET AL 2, 5,47

APPARATUS AND METHOD FOR GRINDING Filed Dec. 29, 1952 5 Sheets-Sheet 5Hag/3 INVENTORS EEUEGE E. fiziMsTzizkjrd HTT NEY United States PatentAPPARATUS AND METHOD FOR GRINDING George E. Comstock 3d, Holden, andGeorge Crompton, Jr., Framingham Center, Mass., assignors to NortonCompany, Worcester, Mass., a corporation of Massachusetts ApplicationDecember 29, 1952, Serial No. 328,464

20 Claims. (Cl. 51-72) The invention relates to apparatus and method forgrinding.

One object of the invention is to provide precision grinding apparatusadapted to remove stock at a high rate and adapted also to produce anexcellent finish. Another object of the invention is to provide aprecision grinding apparatus capable of grinding the hardest ofmaterials at a high rate of stock removal. Another object is to grind athigh rate with minimum heating of the work. Another object is to reducewheel wear.

Another object is to provide simple grinding apparatus givinga high rateof production. Another object is to provide grinding apparatus which canbe embodied in a light weight machine which, at low grinding pressure,will remove stock at a high rate. Another object is to provide a grinderwith apparatus to set a grinding wheel carried thereby in rapid radialvibration. Another object is to produce supersonic vibrations in agrinding wheel. Another object is to provide a grinding wheel capable ofbeing vibrated, preferably supersonically, in a synchronous radialfashion meaning that all around the circumference the vibrations travelin generally radial lines in phase. Another object is to produce in agrinding wheel balanced vibrations or vibrations exerting no resultantthrust on the wheel spindle but not exactly radial. Another object is toproduce standing waves in a grinding wheel for the promotion ofgrinding.

Another object is to incorporate magnetostrictive elements in a grindingwheel whereby a high frequency magnetic field will cause the wheel tovibrate thus to promote grinding action. Other objects are toincorporate such magnetostrictive elements in vitrified wheels, inresinoid bonded wheels and in other types of wheels. Another object isto provide a superior cutting off wheel.

Other objects will be in part obvious or in part pointed outhereinafter.

In the accompanying drawings illustrating some of many possibleembodiments of the mechanical features of this invention,

Figure 1 is a side elevation of a wheel head cross slide unit includingWheel guard and wheel,

Figure 2 is a partial axial sectional view on an enlarged scale of agrinding wheel constructed in accordance with the invention,

Figure 3 is a fragmentary elevation of a portion of the face of thegrinding wheel,

Figure 4 is a sectional view taken on the line 4-4 of Figure 1,

Figure 5 is an elevation of the electromagnetic unit used in anillustrative embodiment of the invention,

Figure 6 is a sectional view illustrating one manner of molding a wheelaccording to the invention, one half of the molding apparatus beingillustrated,

Figure 7 is a side elevation of a wheel head cross slide unit in anotherembodiment of the invention,

Figure 8 is a cross sectional view on an enlarged scale taken on theline 88 of Figure 12,

Figure 9 is a side elevation of the grinding wheel in the secondembodiment of the invention,

Figure 10 is a fragmentary view on an enlarged scale of the wheel ofFigure 9,

Figure 11 is a cross sectional view on an enlarged scale taken on theline 1111 of Figure 9,

Figure 12 is a horizontal sectional view taken on the line 12-12 ofFigure 7 further illustrating the second embodiment of the invention,

t Figure 13 is an elevation of a magnetostrictive grinding wheelillustrating a further embodiment of the inventron,

Figure 14 is a sectional view taken on the line 14-14 of Figure 13.

Referring to Figure 4, a grinding machine base is indicated at 10 andhas a flat way 11 and V-ways 12 supporting complementary shaped portionsof a wheel head-cross slide unit 15. We will not describe a completegrinding machine since the invention is embodied in a grinding wheel andits mounting and these may be components of any type of grinding machineknown, and in some cases (as in some centerless grinding machines) theremay be no cross slide for the grinding wheel.

A wheel spindle 16 is mounted in bearings in the wheel head 15 and thebearings are not illustrated because many satisfactory constructions areknown. Mounted on a tapered portion 17 of the wheel spindle 16 is awheel holding plate 18 engaging an inwardly directed annular flange 19of a grinding wheel 20 which is clamped to the plate 18 by means of aring 21 held to the plate 18 by bolts 22. The plate 18 is shown as keyedto the portion 17 of the spindle 16 and held thereon by means of a nut23. Secured to the spindle 16 at the end opposite the grinding wheel 20is a pulley 24 by means of which the spindle can be driven. Balancingweights 25 held in place by screws 26 are preferably provided to balancethe wheel 20 as vibrations due to unbalance are not wanted, thoseproduced according to the invention being of a different character aswill hereinafter appear. A wheel guard 30 is secured to the head 15 bymeans of bolts 31. Comparing now Figures 1 and 4, a wheel guard cover 32is connected to the wheel guard 30 by means of a hinge 33 and the covercan be locked in closed position by means of a screw Referring now toFigures 4 and 5, we provide a plurality of electromagnets 40. Alternatemagnets are wound in opposite directions so that at one instant thepolarities will be in NSSNNfiS-SN-NS-S-N-N S-S-NNSSNNSS-N arrangementaround the circle and this presupposes an even number of magnets, asshown. To provide this arrangement of polarities it suffices to windadjacent magnets oppositely. A single laminated core 42 with pole pieces43 extends through all of the magnets and this can be made by cuttingthe components from different sized sleeves of soft iron thenvulcanizing the component rings together with rubber having only enoughsulphur to yield a soft rubber. After the core 42 with pole pieces 43has been made, the electromagnet windings 40 are formed by windinginsulated wire between the pole pieces 43. The core 42 is attached totheinside of the cover 32 by means of brackets 45 and screws 46 and 47and thus the electromagnetic unit of Figure 5 is held in place by thecover 32. The tapped holes in the core 42 which receive the screws 46should be coated with an insulating layer of resin or the like.Referring now to Figures 2, 3, and 4, the grinding wheel 20 has thereina ring 50 of magnetostrictive rods embedded in resinous material, suchas phenol-formaldehyde. The axes of the rods are parallel to the axis ofthe wheel 20. The rods can be made of any suitable magnetostrictivematerial of which nickel and an alloy of 45% nickel and 55% iron aregood examples. Magnetostrictive material either expands or contracts ina magnetic field along the axis of the field; nickel and the nickel-ironalloy mentioned have opposite responses under some circumstances so thatone or the other may be used but not both in the same ring. I

Outside of the ring 50 is a wheel zone 51 of abrasive and bond; insideof the ring 50 is a wheel zone 52 of abrasive and bond merging with theflange 19 also made of abrasive and bond. In certain cases the zone 52might be very much smaller relatively than as shown in the drawings.Referring now to Figure 6, one way to make the wheel 20 is as follows:The wheel zone 51 and the ring 50 are separately made. The wheel zone 51is made in the customary-manner for making vitrified bonded grindingwheels which is so well known we need not describe it. The ring 50 isformed and the resin is only partially cured. The wheel zone 51 with thering 50 inside of it are then placed in a mold having a central arbor53, a bottom plate 54, and a top plate in two sections; anouter section55 covering the wheel zone 51 and the ring 50, and an inner section 56to form the zone 52 and flange 19; the bottom plate 54, arbor53 andtheinner section 56 of the top plate being shaped to leave a cavity theexact shape of these parts when the mold is closed. Before the innersection 56 of the top plate is placed on the-arbor 53, the spacetherearound and inside of the ring 50 is filled with a mixture ofabrasive grains and phenol-formaldehyde resin made in the wellknownmanner, then the inner section 56 of the top plate is placed on thearbor and on top of the mixture, and the entire assembly is pressed in ahot press thereby curing the resin under compression to cause the ring50 to be in compression against the zone 51. It is best to use also amold ring 57 gripping the plates 54and-55 during the molding. On'theother hand all three of the flanges 19, the zone 51' and the zone 52 canbe made of abrasive grains bonded withphenol-formaldehyde resin andthese portions can readily be molded integralwith the ring 50 by wellunderstood molding technique. Here again it is preferred to use a' hotpress in order to unite the parts firmly into an integral whole. Ingeneral, whether the zone 51 is vitrified bonded abrasive orphenol-formaldehyde bonded abrasive, we prefer to have a large-volumepercentage of abrasive and a minimum of pores as thereby the vibrations'will be better transmitted.

The continuous windingof the electromagnets 40 is connected totwosources of electric current. The one, known as the biasing current,is direct current. The other is high frequency alternating current inthe supersonic range, that is to say from about 16,000 cycles per secondup to about 200,000 cycles per second. We need not describe how toproducealternating current of frequency in the above range since this isknown technology.

The magnetic flux passes from the pole pieces 43 through the ring 50 toa laminated high permeability ferrous metal ring 60 held by screws 61 tobrackets 62 held by screws 63 to the inside of the wheel guard 30. As inthe case of the tapped holes for the screws 46, it is best to coat thetapped holes for the screws 61 with resin or the like and also toinsulate the ring 60 from the brackets 62. These precautions'minimizeFoucalt or eddy current losses. This ring 60 causes the magnetic flux toflow nearly along the axes of the magnetostrictive rods rather thanacross them because the reluctance is high transverse of the rods andproviding a path of high permeability across the ends of the rods' hasthis result.

Consequently, With the power on, the ring 50 vibrates at supersonicfrequency by expanding and contracting in the direction of the axis ofthe rods of which it is composed. This produces as a resultant radialvibrations in the wheel but since thering 50 is concentric with the axisof the wheel, there is little or no effect upon the hearings in thewheel head 15 nor upon the spindle 16.

- Referring now to Figure 12, it will be noted that it is like Figure 4except that in Figure 4 the section is vertical while in Figure 12 thesection is horizontal. The same wheel head 15 journals the same spindle16 having a tapered portion 17 and the spindle isdriven by the samepulley 24. The grindingwheel 70 is, however, a little different. It has,as better shown in Figures 9, l0 and 11, an outer abrasive portion 71,an intermediate abrasive portion 72, an inner abrasive portion 73, and aflange 74. It further has a pair of rings of rnagnetostrictive rods 75and 76. These may be made in the same manner as the ring 50 and mayconsist of anygood magnetostrictive rods having the same response.Furthermore the wheel can be made by the technique already described inconnection with Figure 6 but with additional molding steps to mold theportions 73 and'74 with the ring 76 in place after the portion 72 hasbeen molded with the ring 75 in place. Thus the outer abrasive portion71 could be vitrified bonded abrasive while the portions 72 and 73 and74could be resin bonded abrasive, or the portions 71, 72, 73 and 74 couldall be resin bonded abrasive. The flange 74 of the wheel 70 is held bythe Wheel holding plate 18 and the ring 21 which is secured to thep1ate'18 by the bolts 22 as in the first described embodiment'of theinvention. Also the plate 18 is secured on the tapered portion 17 bymeans of the nut 23 and furthermore balancing weights 25 held inplace'by screws 26 may be provided.

Still referring to Figure 12, a wheel guard 80 is secured to the wheelhead 15 by means of bolts 81. This wheel guard80 has recessed portions82 receiving insulating blocks 83 made of suitable resin such as phenolformaldehyde resin and embedding horseshoe-shaped electromagnets 84whose pole faces are opposite the ends of the magnetostrictive rods ofthe rings 75 and 76. In this embodiment of the invention the wheel guardcover is mounted on a hinge 91 secured to the wheel guard 80 and, asshown in Figure 7, may be locked in place by means of a bolt 92. Thiswheel guard cover 90 has secured to it metal plates 93 and 94 partiallysupporting blocks 95 of insulating material such as a resin as in thecase of the blocks 83, and these blocks 95 likewise have embeddedtherein horseshoe-shaped electromagnets 96 the pole faces of which areopposite the ends of the magnetostrictive rods of the rings 75 and 76.The resin of the blocks 83 and 95 is molded into stud portions 100 whichproject through the recesses 82 in the case of the blocks 83 and throughthe wheel guard cover 90 in the case of the blocks 95, and nuts 101 onthe stud portions 100 assist in. securing the respective blocks inplace.

. As in the case of the electromagnets 40, the electromagnets 84 and 96are connected to two sources of electric current. One source is thebiasing current and is direct current and the other source is the highfrequency alternating current in the supersonic range from about 16,000cycles per second to about 200,000 cycles per second. The windings andthe electrical connections are made so that at given instants of timethe poles at the opposite ends of the rodsof the rings 75 are oppositepoles and the poles at the opposite ends of the rods of the rings 76 areopposite poles. This describes the polarity due to alternating currentbut furthermore the direct current flows through the windings so thatthe same situation results. continuously, that is to say the polaritydue to the direct current alone is opposite on opposite sides of therings 75 and 76. The alternating current alternately strengthens andcancels the polarity due to the biasing currentwhich makes the rodsvibrate magnetostrictively at the frequency of the A. C. Now if, ineither embodiment of the invention, the peak voltage of the alternatingcurrent is the same as the voltage of the direct current, the magneticfield in the electromagnets goes from zero to full strength due to thecombined currents at the frequency of the A. C. This condition isusually preferred. If the voltage of the D. C. is more than the peakvoltage of the A. C. the field in the electromagnets will strengthen andweaken with the frequency of the A. C. Either of these conditions causesthe magnetostrictive rods to vibrate with the frequency of the A. C. Butif the voltage of the D. C. is less than the voltage of the A. C. therods will vibrate at double the frequency of the A. C. only successivevibrations will be of different amplitudes until the voltage of the D.C. reaches zero in which case the vibrations will all be of the sameamplitude but of double the frequency of the A. C. With a given sourceof A. C. to work with we may sometimes cut out the D. C. power sourcethus to double the frequency in the magnetostrictive rods.

'The electromagnets 40 are connected by wires 102 and 103 as shown inFigure 5. In Figure 4 the ends 105 and 106 of the windings on theelectromagnets 40 are shown. The magnets are thus wound in series. InFigure 1 we show binding posts 107 and 108 to which these ends 105 and106 are connected. These binding posts 107 and 108 extend betweeninsulating washers 109 and hold them in place in opposite sides of ahole through the cover 32. The biasing D. C. and high frequency A. C.sources are connected by wires (not shown) to these binding posts 107and 108. In Figures 7 and 12 we show a pair of wires 110 extending fromthe 'left hand rear magnet'96 to binding posts 111 and 112 respectively,a pair of wires 113' extending to these binding posts respectively fromthe right hand rear electromagnet 84, a pair of wires 114 extending fromthe left hand front electromagnet 96 to the binding posts 111 and 112respectively and a pair of wires 115 extending from the right hand frontelectromagnet 84 to the binding posts 111 and 112 respectively and byconnecting wires, not shown, the biasing current and the high frequencycurrent are connected to these binding posts 111 and 112 and thus theelectromagnets 84 and 96 may be energized in the manner hereindescribed. In the embodiment of Figures 7- and 12 the electromagnets areconnected'in parallel.

Considering now the vibration of the-wheels, we p'refer that they shallvibrate in resonance with one node at the axis of the wheel. This resultcan be achieved by causing a wheel to vibrate at its fundamentalfrequency across its diameter, or at any harmonic thereof. The fact thatwe can use harmonics greatly extends the versatility of this inventionfor the diameter of the grinding wheel could be from three or fourinches to thirty or forty inches. In many machine tool grinding machinesthe grinding wheels are large, frequently thirty inches in diameter whenthey are new, and to cause such wheels to vibrate in resonance withoutusing frequencies in the sonic range we must, in many cases, make use ofa harmonic of the fundamental frequency.

We desire to avoid the sonic frequencies for two reasons. In the firstplace, in general, vibrations in the sonic frequencies do not aid thegrinding operation as much as do vibrations in the supersonicfrequencies. In the second place sonic frequency vibrations involveaudible sound, which could be very loud, and this would be distressingto the operator and others in the vicinity of the grinder.

Electrical apparatus for delivering electric energy at supersonicfrequencies is usually adjustable to vary the frequency over quite awide range and so therefore we can achieve our objective of causing thewheel to vibrate in resonance. Resonance is indicated by the action ofan ammeter in one of the circuits of the high frequency generator; whenthe ammeter reading suddenly rises while tuning the frequency, it is asign that a resonant frequency has been reached.

But this resonant frequency may, in some cases, be the resonantfrequency of the magnetostrictive rods in the ring or rings and we canoperate the machine satisfactorily on this resonant frequency. It is inmost cases a matter of which frequency delivers the most power to thewheel and this can be determined by the ammeter. Even if, with one ormore rings of rods in resonance and the wheel not in resonance the axisof the wheel is no longer at a node, the effect upon the wheel spindle16 is small due to the fact that in each embodiment the electromagnetsand the rings are located symmetrically and in circles coaxial with thewheel and its spindle, so that wave impulses on one side are cancelledby wave impulses on the other side all around the axis.

In the first described embodiment more power can be put into the wheelthan in the second embodiment due to the greater number ofelectromagnets in the first embodiment. And in the first embodiment agreater amount of power can be used. But'in the second embodiment thepower is to a large extent concentrated where it is most effective. Itwill be understood that the resultant vibrations perpendicular to theaxis of the wheel spread out in all directions in the planeperpendicular to such axis. For that reason there is also some loss inthe second embodiment and if the power is available it is preferred tovibrate the wheel all around the circle.

High frequency, especially supersonic, vibrations have an eroding effecton work pieces, especially hard and brittle work pieces. Thus inaccordance with the invention the work piece is both ground and erodedby vibrations. Furthermore the vibrating blows delivered by the abrasivegranules are believed to create an entry for them into the work piecethereby assisting the'grinding action. Usually we use grinding coolant,preferably water which may have a rust inhibitor therein. Water or othercoolant is delivered to the grinding line between work piece 116 (seeFigure 12) and the wheel by the usual nozzle 117 (Figures 1 and 12).Supersonic vibrations cause, in the presence of water, cavitation whichhas a strongly erosive etfect and the high rate of cutting hard workpieces may be in part due to cavitation.

Grinding wheels supersonically excited in accordance with the inventionwill grind all materials that can be ground at all but the materialremoved factor is increased most markedly and to the greatest extentwhen hard brittle materials such as the hard carbides, oxides, borides,nitrides and silicides are ground. Some of these materials can hardly beground at all with wheels the abrasive of which is aluminum oxide. Someof these materials, such as boron carbide, can hardly be ground at allwith wheels the abrasive of which is silicon carbide. But we can grindboron carbide with supersonically vibrated silicon carbide abrasivegrinding wheels.

The part of the wheel which grinds (51 in Figure 2 and 71 in Figures 9,and 11) can be made of abrasive bonded with any known bond, such asvitrified bond and phenol-formaldehyde bond already mentioned, alsoaniline-formaldehyde resin bond, alkyd resin bond, magnesium oxychloridebond, rubber bond, butadiene acrylic nitrile copolymer bond, butadienestyrene copolymer bond, shellac bond, glass bond and sodium silicatebond. The abrasive can be aluminum oxide of any variety-- fused aluminaregular or white or in discrete crystals or corundum or emery; or it canbe silicon carbide of any varietygreen, gray or black, or diamonds canbe used. It is preferred to use bonds which transmit sound with avelocity as near to that at which the abrasive transmits it as possible;hence the vitrified type of bond is usually preferred.

Referring now to Figures 13 and 14, we therein illustrate the inventionembodied in a cut-off wheel 120. This wheel can be made by bondingabrasive, for example fused alumina or silicon carbide, withphenolformaldehyde resin and it is preferable to use a large volumepercentage of abrasive and to hot press the wheel to get a strongabrasive packing which will well transmit the vibrations. We makemagnetostrictive units 121 each one of which comprises a pair ofplurality of plates 122 of highly permeable ferrous metal, the platesbeing separated and bonded together by resin or vulcanized rubber or thelike, and a rectangular parallelepiped collection of magnetostrictiverods 123 interposed between each pair of collections of plates 122. Agrinding machine is provided like that shown in Figure 12 with horseshoeelectromagnets 84 and 96 on either side of the wheel 120 and we mighthave as many electromagnets 84 and as many electromagnets 96 as thereare magnetostrictive units 121, in this case 16. The polarity and thewindings can be arranged as already explained in connection with Figure12 so that at a given instant of time the polarity may be as shown inFigure 14 where north poles are opposed to south poles so that themagnetic flux must flow into the plates 122 and through themagnetostrictive rods 123. It will be noted that in this embodiment ofthe invention the rods vibrate radially of the wheel which is the mosteffective condition. Wheels constructed along the lines of Figures 13and 14 can also be used for other kinds of grinding operations, that isto say they are in nowise limited to use as cutting off wheels but maybe used for cylindrical grinding, surface grinding and in many othergrinding operations. Of course, as in other embodiments of theinvention, the magnets 84 and 96 are energized by alternating currentwith supersonic frequency and preferably also by biasing direct current.

It will be seen that the bonds mentioned are all of them non-conductorsof electricity. Any electrical non-conductive bond can be used sotherefore we should not be limited to particular ones. Metal bondscannot be used because they would absorb the power by the creation ofeddy currents. In fact they would quickly heat up. But the bond couldhave metal particles insulated from each other as in the wheel mountingof Van der Pyls U. S. Patent No. 2,150,886 because in such a bond theeddy currents would only be minute. In every case our bond is a maturedbond, meaning it is heat set.

It will be seen that in the embodiment of the invention illustrated inFigures 2, 3, 9, 10 and 11 the magnetostrictive rods are parallel to theaxis of the wheel while in the embodiment illustrated in Figure 13 themagnetostrictive rods extend practically radially of the wheel. Howeverin each embodiment of the invention the magnetostrictive rods areperpendicular to a radius line of the wheel at a point degreescircumferentially from their location therein.

It will thus be seen that there has been provided by this invention anapparatus and method for grinding in which the various objectshereinabove set forth together with many thoroughly practical advantagesare successfully achieved. As many possible embodiments may be made ofthe above invention and as many changes might be made in the embodimentsabove set forth it is to be understood that all matter hereinbefore setforth or shown by the accompanying drawings is to be interpreted asillustrative and not in a limiting sense.

We claim:

1. A grinding wheel of abrasive material composed of abrasive grainsbonded together with matured electrically non-conducting bondingmaterial, said wheel being circular, and a ring of magnetostrictivemetal which is at least 45% nickel embedded in said wheel in a positioncoaxial withthewheeland integrallybonded to the abrasive material.

2. A grinding wheel acccrding to claim 1 in which the ring ofmagnetostrictive metal 'is a ring of magnetostrictive metal rods theaxes of which are substantially parallel to the axis of the wheel.

3. A grinding wheel according to claim 2 in which theire are a pluralityof rings of magnetostrictive metal ro s.

4. A grinding wheel according to claim 1 in which there are a pluralityof rings of magnetostrictive metal. 5. A grinding wheel of abrasivematerial composed of abrasive grains bonded together with maturedelectrically non-conductive bonding material, said wheel being circular,and a plurality of sets of magnetostrictive .rods of metal which is atleast 45% nickel embedded in said wheel with each set of rodsperpendicular to the axis of the Wheel.

6. A grinding wheel according to claim 5 in which at each end of eachset of rods there is a mass of mag f netically highly permeable metal.

7. A grinding wheel according to claim 6 in. which the sets of rods forma ring of sets coaxial with the wheel radially of the wheel.

8. A grinding wheel according to claim 5 in which the ofmagnetostrictive metal embedded in said wheel said ring being coaxialwith said wheel and said rods being parallel to the axis of said wheel.

10. Grinding apparatus comprising a grinding wheel comprising abrasivegrains bonded together with electrically non-conducting bonding materialand containing magnetostrictive metal elements, and electromagneticmeans arranged about said spindle in geometrically balanced positionsrelative to the axis of said spindle with the poles of theelectromagnetic means close to the locus of a side of said grindingwheel and said poles being so positioned that the lines of force willpenetrate said wheel to vibrate said magnetostrictive elements embeddedtherein when the electromagnetic means is excited with high frequencyalternating current.

11. Grinding apparatus according to claim 10 in which theelectromagnetic means consists of horseshoe magnets.

12. Grinding apparatus comprising a wheel spindle, a grinding wheel onsaid spindle, said grinding wheel being composed of abrasive grainsbonded together with matured electrically non-conductive bondingmaterial, said wheel being circular, a plurality of magnetostrictiveelements embedded in said wheel, electromagnetic means arranged aboutsaid wheel on at least one side thereof with the poles of theelectromagnetic means close to said side and said poles being sopositioned that the lines of force penetrate said wheel and fiow throughthe magnetostrictive elements embedded therein, whereby when saidelectromagnetic means is connected to a source of high frequencyalternating current said magnetostrictive elements will vibrate at highfrequency.

13. Grinding apparatus according to claim 12 in which theelectromagnetic means is embodied in an even number of electromagnetsarranged symmetrically of the wheel with respect to the axis of thespindle with each electromagnet diametrically opposite one on the otherside at the same distance from the axis.

14. Grinding apparatus according to claim 13 in which themagnetostrictive means includes rods which are perpendicular to a radiusline of the wheel at a point degrees circumferentially from theirlocation therein.

15. Grinding apparatus according to claim 14 in which themagnetostrictive means includes radial rods.

16. Grinding apparatus comprising a wheel spindle, grinding wheel onsaid spindle, said grinding wheel being composed of abrasive grainsbonded together with matured electrically non-conductive bondingmaterial, said wheel being circular, a plurality of magnetostrictiverods parallel to the axis of said wheel embedded in said wheel,electromagnetic means arranged about said wheel on at least one sidethereof with the poles of the electromagnetic means close to said sideand said poles being so positioned that the lines of force penetrate thewheel and flow through the magnetostrictive' rods embedded therein,whereby when said electromagnetic means is connected to a source of highfrequency alternating current said magnetostrictive rods will vibrate athigh frequency.

17. Method of grinding consisting in rotating a grinding wheel ofabrasive material composed of abrasive grains bonded together withmatured electrically nonconducting bonding material, said wheel being acircular disc, and coincidentally vibrating said wheel in the plane ofthe disc with vibrations which are canceled at the axis of the wheel buttravel to the periphery thereof, said grinding wheel grinding a workpiece placed against its periphery, the frequency of said vibrationsbeing above 16,000 cycles per second.

18. Method of grinding according to claim 17 in which liquid principallyconsisting of water is flowed to the locus where the periphery of theWheel is in contact with the work piece.

19. Method of grinding consisting in rotating a grinding wheel which isa circular disc while coincidentally vibrating said wheel in the planeof the disc with vibrations which are canceled at the axis of the wheelbut travel to the periphery thereof, said grinding wheel grinding a workpiece placed against its periphery, the frequency of said vibrationsbeing above 16,000 cycles per second.

20. Method of grinding according to claim 19 in which liquid principallyconsisting of water is flowed to the locus where the periphery of thewheel is in contact with the work piece. 1

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